This disclosure pertains to stages and the like as used in charged-particle-beam (CPB) lithographic-exposure systems such as xe2x80x9cdirect-drawingxe2x80x9d and xe2x80x9cprojectionxe2x80x9d exposure systems. CPB direct-drawing systems are used mainly for, e.g., manufacturing masks and reticles as used in optical and CPB microlithography apparatus and methods. CPB projection exposure systems are any of various CPB microlithography apparatus used principally in the manufacture of microelectronic devices such as integrated circuits, displays, thin-film magnetic heads, and micromachines.
Charged-particle-beam (CPB) direct-drawing lithography systems literally draw a pattern using a charged particle beam such as an electron beam. These systems, and their associated methods, are used mainly for drawing a pattern to be defined on a mask or reticle (generally termed a xe2x80x9creticlexe2x80x9d herein). CPB projection-lithography systems project an image of a pattern, defined on a reticle, onto a substrate (e.g., semiconductor wafer) that has been xe2x80x9csensitizedxe2x80x9d so as to be imprintable with the image. In both general types of lithography systems, one or more stages are used to hold and controllably move the substrate and, if one is used, the reticle. Specifically (e.g., in a CPB projection-lithography system), a xe2x80x9creticle stagexe2x80x9d supports and moves a reticle, and a xe2x80x9cwafer stagexe2x80x9d supports and moves a substrate. Each such stage is generally termed a xe2x80x9cstage.xe2x80x9d
Various approaches have been considered for driving a stage. In a conventional CPB direct-drawing system, a common approach involves driving the stage using a motor connected to the stage using a mechanical power-transfer mechanism such as a ball screw for transforming rotational motion of the motor into linear motion of the stage. Unfortunately, power-transfer mechanisms such as ball screws capable of achieving finely controlled motion of the stage actually are quite complex and disadvantageously generate fine dust particles that contaminate the reticle or substrate held by the stage.
To counter the problem posed by motors and ball screws, the use of gas-based actuators, such as air cylinders, has been proposed. Modern CPB lithographic-exposure systems, however, must be capable of accurately transferring pattern elements that are only 100 nm wide or less, with satisfactorily high throughput, operating speed, and accuracy of establishing and maintaining stage position. Gas-based actuators simply are incapable of meeting these requirements.
In response to the need for better stage actuators, actuators based on linear motors have come recently into use. Linear motors that contain permanent magnets, however, have a problem in that the charged particle beam is adversely affected by the magnetic field generated by the permanent magnets. If the lithography system is to be used for forming a 100-nm linewidth pattern on a wafer or other substrate at high throughput, the effects of the magnetic field generated by the permanent magnets in the linear motor cannot be ignored.
Two types of linear motors are in current use. In a moving-coil (MC) linear motor, the permanent magnet is provided on the xe2x80x9cstatorxe2x80x9d side, and a coil is provided on the xe2x80x9carmaturexe2x80x9d or xe2x80x9cmoving memberxe2x80x9d side. In a moving-magnet (MM) linear motor, the permanent magnet is provided on the moving member side, and a coil is provided on the stator side.
Of these two types of linear motors, in the MC type, the magnetic field created by the permanent magnet remains constant. During an actual lithographic exposure, no current flows in the coil. The coil either does not generate a magnetic field, or generates a magnetic field that is exceedingly small compared with the magnetic field generated by the permanent magnet. Hence, it is relatively simple to compensate for the effects on a CPB optical system of the magnetic field generated by the linear motor. Nevertheless, to facilitate compensation, it is desirable to reduce the magnetic field generated by the linear motor, especially in the vicinity of the optical axis of the CPB optical system.
MC-type linear motors also are disadvantageous because the coils (which generate heat during operation and require cooling) are difficult to cool. I.e., a coil located on a moving component requires that the coolant be supplied to the coil via a flexible conduit. The necessary flexibility of the conduit results in unstable positional control of the linear motor. For these reasons, it more desirable to use an MM-type linear motor for stage movement.
MM-type linear motors have a drawback in that the magnetic field generated by the permanent magnet, as experienced at the optical axis, changes with movement of the stage. This change in the magnetic field can cause problems with controlling the charged particle beam propagating through the CPB optical system. Correcting this problem at the CPB optical system requires a changing magnitude of correction, depending upon stage position, which is essentially impossible to accomplish.
In view of the shortcomings of conventional apparatus and methods as summarized above, an object of the present claims is to provide a stage for a charged-particle-beam CPB exposure system, wherein any impact of the magnetic field generated by a stage-driving linear motor on the CPB optical system is minimized.
To such end, stage assemblies are provided for CPB lithographic-exposure systems. An embodiment of such an assembly comprises a stage configured for holding a reticle or substrate. The stage extends in an X-Y plane perpendicular to an optical axis that is parallel to a Z axis. The assembly also includes a linear motor operatively coupled to the stage and configured for moving the stage in the X-Y plane. The linear motor comprises a permanent magnet split into multiple permanent-magnet subunits arranged symmetrically with respect to a plane that is perpendicular to the X-Y plane. The linear motor can be a moving-coil type or moving-magnet type of linear motor. Also, the first and a second permanent-magnet subunits produce respective first and second magnetic fields that desirably cancel at least a portion of each other at the optical axis.
By splitting the permanent magnet into two or more subunits, each subunit can be disposed farther from the optical axis (i.e., laterally farther from the CPB optical system) than the permanent magnet in a conventional linear motor in a stage assembly. Such a configuration minimizes the impact of the magnetic field generated by the subunits CPB optical system.
A stage assembly according to another embodiment comprises a stage as summarized above. The stage assembly also includes a moving-coil type of linear motor operatively coupled to the stage. The linear motor comprises first and second linear-motor portions that are disposed in respective positions that are symmetric with respect to a plane including the optical axis and extending perpendicularly to the X-Y plane and parallel to the movement direction of the stage. Each linear-motor portion comprises a respective permanent magnet split into multiple respective magnet subunits, wherein the magnet subunits of the first linear-motor portion are disposed relative to the magnet subunits of the second linear-motor portion in a point-symmetrical manner with respect to a point at which the X-Y plane intersects the optical axis.
I.e., in a 3-dimensional rectangular coordinate system in which the optical axis is designated as the Z-axis, if the central axis for a linear motor is on the X-Y plane and the linear motor drives the stage in the Y-direction, then the linear-motor portions are disposed in positions that are plane-symmetrical with respect to the Y-Z plane that passes through the optical axis. Because the respective permanent magnets of each linear-motor portion are each split into two or more respective magnet subunits, the magnet subunits of a first linear-motor portion are disposed with respect to the magnet subunits of a second linear-motor portion so as to be point-symmetrical relative to the point (i.e., the origin) at which the X-Y plane containing the respective central axes for the linear-motor portions intersects with the optical axis.
In other words, the permanent magnet in the first linear-motor portion and the corresponding permanent magnet in the other linear-motor portion are disposed point-symmetrically with respect to the origin. In this arrangement, on the optical axis, a magnetic field in any direction in 3-dimensional space assumes a substantially zero magnitude due to the cancellation of the magnetic fields associated with the coils of the linear-motor portions. Thus, the impact of the magnetic field, generated by the magnet subunits in the linear-motor portions, on the CPB optical system is minimized.
A stage assembly according to yet another embodiment comprises a stage as summarized above. The stage assembly also includes a moving-magnet type of linear motor operatively coupled to the stage for moving and positioning the stage in a movement direction in the X-Y plane. The linear motor comprises multiple permanent-magnet subunits and multiple corresponding dummy permanent-magnet subunits. The magnet subunits and the dummy-magnet subunits are arranged so as to move symmetrically with respect to a plane that is perpendicular to the movement direction and that includes the optical axis. Each of the permanent-magnet subunits and the dummy permanent-magnet subunits has respective magnetic poles. In this embodiment, if the Z-axis is perpendicular to the X-Y plane, the optical axis is parallel to the Z-axis, and the movement direction of the stage is the Y-axis direction, then the plane that is perpendicular to the movement direction and that includes the optical axis is an X-Z plane. In this configuration the respective magnetic fluxes from each permanent magnet subunit that moves the stage and from the respective dummy permanent magnet corresponding to the particular permanent magnet subunit cancel each other on the X-Z plane. As a result, even if the permanent magnet subunit moves in the movement direction, the magnetic flux from the permanent magnet subunit as experienced on the optical axis is substantially zero. A key benefit of this configuration is that the magnetic fields produced by the permanent magnets used to drive the stage have substantially no effect on the charged particle beam propagating in an axial direction through the CPB optical system.
As an alternative to the configuration summarized in the preceding paragraph, the respective magnetic poles of the permanent magnet subunits and of the dummy-magnet subunits can be disposed symmetrically with respect to the plane that is perpendicular to the movement direction and that includes the optical axis.
The following is further with respect to the xe2x80x9cplane that is perpendicular to the movement direction and that includes the optical axis.xe2x80x9d By way of example, if the stage is driven in the Y-axis direction, and if the magnetic poles for one of the permanent magnets that move the stage in the Y-axis direction are oriented (toward the positive Y-axis direction) with N-S-N-S . . . poles on the top and S-N-S-N . . . poles on the bottom, then the magnetic poles for the corresponding dummy permanent magnet are oriented (toward the negative Y-axis direction) with N-S-N-S . . . poles on the top and S-N-S-N . . . poles on the bottom. Such an arrangement of magnetic poles allows the respective magnetic fluxes (in the movement direction) between each stage-moving permanent magnet and its corresponding dummy permanent magnet to cancel each other, and thus to produce a substantially zero-magnitude magnetic flux at the optical axis. Even if the permanent-magnet subunit moves, the effect of the magnetic field (in the movement direction) generated by the permanent-magnet subunit on the CPB optical system is extremely small.
Alternatively, the respective magnetic poles of the stage-moving magnet subunits and of the dummy-magnet subunits can be disposed anti-symmetrically with respect to the plane that is perpendicular to the movement direction and that includes the optical axis. In this alternative configuration, the xe2x80x9cplane that is perpendicular to the movement direction and that includes the optical axisxe2x80x9d is the same as summarized above. The term xe2x80x9canti-symmetricallyxe2x80x9d means that the respective magnetic poles for each of the stage-moving magnet units and their respective dummy-magnet subunits are in mutually symmetrical positions, but each respective dummy-magnet subunit is rotated 180 degrees around the center line of its movement direction. For example, for moving the stage in the Y-axis direction, the magnetic poles for each permanent-magnet subunit are oriented in the positive Y-axis direction as N-S-N-S . . . on the top and S-N-S-N . . . on the bottom, and the magnetic poles for each respective dummy-magnet unit are oriented in the negative Y-axis direction as S-N-S-N . . . on the top and N-S-N-S . . . on the bottom. With such a configuration, the respective magnetic fluxes (in the direction of the optical axis) of each stage-moving permanent-magnet subunit and its respective dummy-magnet subunit cancel each other and hence produce a substantially zero-magnitude magnetic flux at the optical axis. As a result, even if the permanent-magnet subunit moves, the effect of its magnetic field in the movement direction on the CPB optical system is extremely small.
Yet another embodiment of a stage assembly comprises a stage as summarized above. The stage assembly also includes first and second moving-magnet linear motors operatively coupled to the stage for moving and positioning the stage in a movement direction in the X-Y plane. The linear motors are disposed in respective positions that are symmetric with respect to a plane that is parallel to the movement direction and that includes the optical axis. Each linear motor comprises: (1) a stage-moving permanent magnet split into a respective set of multiple magnet subunits and (2) a respective set of multiple corresponding dummy permanent-magnet subunits that are arranged and configured to move symmetrically with respect to a plane that is perpendicular to the movement direction and that includes the optical axis. The stage-moving magnet subunits of the first linear motor are arranged and configured to move symmetrically with the dummy-magnet subunits of the second linear motor, and the stage-moving magnet subunits of the second linear motor are arranged and configured to move symmetrically with the dummy-magnet subunits of the first linear motor, relative to the optical axis. The stage-moving magnet subunits of the first linear motor and the dummy-magnet subunits of the second linear motor, and the stage-moving magnet subunits of the second linear motor and the dummy-magnet subunits of the first linear motor are disposed anti-symmetrically with respect to the plane that is perpendicular to the movement direction and that includes the optical axis.
For example, in a rectangular coordinate system in which the optical axis is designated as the Z-axis, if the stage is moved in the Y-axis direction in the X-Y plane, the two linear motors are plane-symmetric relative to each other with respect to the Y-Z plane. In each linear motor, the permanent magnet that moves the stage is split into two or more magnet subunits. Also, corresponding dummy permanent magnets are provided that are plane-symmetric relative to the respective stage-moving permanent magnets with respect to the X-Z plane. As a result, the dummy permanent magnets move plane-symmetrically with respect to the X-Z plane.
Between the two linear motors, the permanent magnets are positioned such that each stage-moving permanent magnet moves by maintaining an axis-symmetrical position relative to the respective dummy permanent magnet for the other linear motor, with respect to the Z-axis.
The respective magnetic poles for the stage-moving permanent magnets and for the dummy permanent magnets are oriented anti-symmetrically with respect to the plane that is perpendicular to the movement direction and that includes the optical axis. Thus, regardless of the position of the stage, the magnetic fields in either direction on the optical axis are canceled and are substantially zero. As a result, even in instances in which MM-type linear motors are used, the effects of the magnetic fields produced by the permanent magnets on the CPB optical system are substantially eliminated.